1. Field of the Invention
The present invention relates to a composite integrated semiconductor device in which there are integrated on the same semiconductor substrate different circuits such as an input surge/noise absorbing circuit for absorbing surge or noise, an attenuating/level-shifting circuit providing attenuation or level-shifting operations, and an electrical signal converting circuit providing an electrical signal converting operation. In particular, the present invention relates to a composite integrated semiconductor device that inputs a signal without surge and noise to a control unit controlling, for example, the electrical equipment of an automobile, with the electric potential level of the signal being matched to the electric potential level of the control unit.
2. Description of the Related Art
Conventionally, circuits such as a surge/noise absorbing circuit for absorbing surge or noise, an attenuating/level-shifting circuit providing an attenuating or a level-shifting operation, an electrical signal converting circuit providing an electrical signal converting operation, etc., are connected to an input side of an electrical control unit (ECU) that controls the electrical equipment of, for example, an automobile. These circuits permit the inputting of a signal without surge and noise, with an electric potential level of the signal matched to an electric potential level of the control unit. FIG. 16 is a block diagram schematically showing a conventional configuration of these functional circuits.
As shown in FIG. 16, a plurality of discrete components 1 such as resistors, capacitors, and diodes are combined, as required, and mounted on a printed circuit board (not shown). External electrical input signals 2 are supplied through the discrete components 1 forming the functional circuits and output as electrical output signals 3, which are supplied to the input terminals 5 of a semiconductor device 4 without surges and noise. Each of the signals is matched to a driving electric potential level of the semiconductor device 4.
In the conventional configuration as described above, however, realization of the circuits having the desired functions has been achieved using a large number of the discrete components 1. This has resulted in an increase in the mounting area of a printed circuit board, and an associated increase in the number of man-hours required to mount the components.